arm64: dts: rockchip: fix typo in iommu nodes

The latest dtc warns about an extraneous cell in the interrupt
property of two of the iommu device nodes:

Warning (interrupts_property): interrupts size is (16), expected multiple of 12 in /iommu@ff373f00
Warning (interrupts_property): interrupts size is (16), expected multiple of 12 in /iommu@ff900800

This removes the typo.

Fixes: cede4c79 ("arm64: dts: rockchip: add rk3368 iommu nodes")
Fixes: 49c82f2b

 ("arm64: dts: rockchip: add rk3328 iommu nodes")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>